1. Field of the Invention
The present invention pertains to obtaining core samples from a subterranean formation through a producing well using coilable tubing or a snubbing unit to run the drilling and coring tools.
2. Background
Producing oil and gas from subterranean formations through wellbores sometimes requires inspection of formation conditions to analyze production characteristics and prescribe future production techniques. Analysis of formation characteristics or changes is usually dependent on the ability to take suitable core samples of the formation in the vicinity of the wellbore. Conventional coring operations require that the well be shut in while a drilling rig is brought in and operated to perform the coring operation. This process is time consuming and expensive and effectively requires shut-in of the well during all phases of the drilling and core sample acquisition process.
Moreover, limitations on minimum core diameter have, heretofore, precluded obtaining conventional core samples through small diameter tubing strings and other wellbore structures of a diameter less than conventional casing diameters thereby, again, requiring the use of a drilling rig to pull the tubing strings and provide a drillstring for obtaining a core sample of sufficient diameter to prevent invasion of the core center. Conventional sidewall coring techniques are limited to a few inches of depth of investigation of the formation from the wellbore and the cores are often too small in diameter and length to be useful.
An improved method for minimizing the invasion of fluids into a core is described in a U.S. patent application entitled: Method for Obtaining Cores From a Producing Well by Eric W. Skaalure, and improved apparatus for obtaining cores is described in a U.S. patent application entitled: Permanent Whipstock and Placement Method by David D. Hearn, et al, both assigned to the assignee of the present invention and both of even filing date with this application. The present invention overcomes the disadvantages of conventional coring while providing an improved and unique method for obtaining core samples from and through a production well.